#include <fstream>
#include <deque>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

const int NMAX=5e6+5;
int n, k, v[NMAX];
long long s;
deque<int> dq;

int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;i++)
        cin>>v[i];
    for(int i=1;i<k;i++)
    {
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    for(int i=k;i<=n;i++)
    {
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
        while(dq.front()<i-k+1)
            dq.pop_front();
        s+=1LL*v[dq.front()];
    }
    cout<<s;
    return 0;
}